Cavity resonator electron discharge apparatus



R. P. STONE CAVITY RESONATOR ELECTRON DISCHARGE APPARATUS May 243, 195o Filled July 29, 1944 k l I Ezy.

cir/fao: @/Qcu/r 747.276

Patented May 23, 1950 CAVITY RESONATOR ELECTRON DISCHARGE APPARATUS Robert P. Stone, Griggstown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application July 29, 1944, Serial No. 547,190

14 Claims.

My invention relates to electron discharge devices and associated circuits, more particularly to such devices and circuits useful at very high frequencies.

An object of my invention is to provide an electron discharge device and associated circuit particularly suitable for high frequency operation and capable of delivering large amounts of power.

A further object of my invention is to provide an electron discharge device and associated circuits of the cavity resonator type having an improved coupling means for providing feedback when the device is to act as an oscillator.

More specifically it is an object of my invention to provide a coupling means the reactance of which can be tuned out to increase the power output of the device and thus increase efficiency.

These and other objects will apear hereinafter.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood -by reference to the following description taken in connection with the accompanying drawing in which Figure 1 is a longitudinal section of an electron discharge device and associated circuit incorporating my invention, Figure 2 is a partial lonitudinal section taken along the line II-II of Figure 1, and Figure 3 is an equivalent circuit diagram of circuits utilizing the apparatus shown in Figure 1.

In Figure 1 is shown an electron discharge device and circuit described and claimed in a copending application of Leon S. Nergaard, Serial No. 516,388, filed December 31, 1943, now Patent No. 2,461,125, dated February 8, 1949, and assigned to the same assignee as the present application. It consists of a triode electron discharge device specially adapted and designed to cooperate with cavity resonator type circuits. Briefly the electron discharge device comprises essentially a cathode, grid and anode of the coaxial type, the anode forming part of the tube envelope. The grid and cathode are provided with specially designed terminals cooperating with and merging into the circuits proper. Connected between the grid and cathode is a coaxial linetype resonator which provides the input circuit, and coupled between the anode and grid is another coaxial line resonator of the half-wave open line type which provides the output circuit. The input resonator is tuned by means of a specially designed tuning condenser and energy is taken from the input circuit. According to my invention, I provide a specially designed coupling means which couples the input and output resonators and is provided with means for tuning the coupling means to increase the eciency of operation.

The electron discharge device per se will be described before the apparatus as a whole. The electron discharge device includes the inverted cup-shaped cathode I0 provided with the heater i I. A cup-shaped grid comprising a cap I2' and grid wires I2 encloses the cathode and is coaxial therewith. An inverted cup-shaped anode I3, preferably formed from a copper block, encloses the cathode and grid and is coaxial with the latter two electrodes. For cooling purposes radiating -fins I4 are fastened, preferably by cadmium soldering, to the anode block.

The grid is supported on a cone-shaped supporting member I5 secured to the flange I6. The anode is provided with a ring-like sealing member I'I of inverted U-shaped transverse section. Sealed between the outer leg of the member I1 and the flange I6 is the insulating collar I8 preferably of glass. The cathode is supported on a tubular member I9 by means of the fingers 20 sealed between the cup-shaped member I0 and the closure member 2| of the cathode. These fingers reduce the heat conduction from the cathode to the cathode support I9, at the same time providing rigid support for maintaining proper spacing between the cathode and grid. One end of the cathode heater II is electrically connected to the cathode cup I Il and the other provided with a lead 22 sealed through the end of the tubular member I9. The tubular member I9 is in turn hermetically and insulatingly sealed to the flange I6. The ange I6 is in turn provided with a radially extending transverse flange 25 for purposes to be described. A getter element 26 is connected between the tubular member I9 and the lead 26 sealed through the end of the tubular member I9. Thus the grid and cathode are hermetically sealed within a vacuum-tight space which may be evacuated through the sealed off tubulation 28.

The element I I' supports the element 29 which may be utilized to increase the cathode-anode capacity for feedback purposes if desired. Element 29 could be eliminated and all of the desired feedback obtained in a manner to be described..

The cathode cylinder is extended with a copper thimble or elongated cup-shaped member 3l. This member slides over and is secured to the cathode support I9 and is provided with slots for receiving the seals of conductors 25 and 22. The heater lead 22 is extended by means of the conductor 36 to the jack pin 34 insulated from member 3|. This thimble results in the protection of the exhaust tubulation and heater and getter leads, provides a cathode terminal which can be plugged into an appropriate socket in a transmission line and brings the heater lead out on the axis of symmetry so that the tube can be plugged into the circuit Without reference to its angular position.

The assembled high frequency apparatus for generating an ultra high frequency power output and utilizing an electron described, is shown in Figure 1. The input circuit is of the coaxial line cavity resonator type coupled between the grid and the cathode, the end remote from the grid and cathode being closed.

This circuit comprises an outer tubular member 40 and inner tubular member 4| electrically connected together and closed by means of the conducting disc 42. Transverse disc 43 is electrically and mechanically secured to the tubular member 40 and is provided with a shoulder or shelf 44 for receiving the grid ring or flange 25 of the tube.

Supported on the member 43 are a plurality of sliding clamps 45 and 45 which can be slid transversely of the longitudinal axis of the electron discharge device to secure the grid ring to this member. They are slidably retained by means of the screw elements which can be tightened when the grid flange is in place. Thus there is a direct electrical connection between the outside tubular member 40 and the grid, permitting the grid to be operated at ground potential. This arrangement also gives good thermal contact to the grid flange, thus reducing the grid temperature. The cathode is capacitively coupled to the inner tubular member. Mounted within the inner tubular member 4| is the tubular member 50, preferably of mica and a second tubular member 5|, which is conducting and provided with a cup-shaped portion 54 having spring fingers 52 thereon engaging the outer surfaces of the cathode thimble 3|. This arrangement capacitively couples the cathode to the inner tubular member.

The cathode heater is supplied by means of the conductors 55 and 56. The conductor 55 is electrically connected to inner tubular member 5| in turn providing a circuit to one side of the cathode heater through fingers 52, cathode thimble 3|, cathode lead and support I9, to the ribbon-like supports 2U, to one side of the cathode, back through the cathode heater conductor 22, conductor 36, pin 34, jack 53, which is insulatingly supported by insulation 54 within the cup-shaped member 54.

The tank circuit coupled between the grid and the anode is of the coaxial half wave open line type and includes the inner tubular member 6|! of cup-shape and secured to the anode radiator by means of screw 6| and provided with curved-in lip 6U' for reducing corona losses. The outer tubular member 59 is mechanically and electrically secured to the grid support 43. The member 59 extends beyond the end of member 60 to prevent radiation from the open end of the line. The cylinder 5i? can be closed at its open end provided the closure is made about a diameter of 60 from the end of 6D. This provides a half wave cavity resonator and because of its arrangement it can be made larger than the closed type and thus reduces the possibility of serious voltage break-down problems which would occur with 4 small size cavity resonators maintained to operate, for example, at frequencies higher than 600 megacycles.

While the apparatus could be operated as' an amplifier, I prefer to utilize it as an oscillator and for this purpose I provide the member 43 with an aperture 43 to permit the use of feedback coupling means consisting of tubular element 1D and tubular element in which is telescopically supported the U-shaped coupling loop member 12, the length of which can be varied to determine the amount of coupling desired. The coupling loop portion 13 of the element within the anode tank circuit is formed as shown to reduce sharp corners and remove the loop as far as possible from the high voltage field of the anode.

In order to tune out the inductive reactance of the coupling loops '|2 and |3, in accordance with my invention I provide a tuning stub consisting of the inner conductor '|4 and the outer tubular member 15 with a tuning ring '|6 therebetween slidable axially by means of the operating handle This increases the power output and efficiency considerably. The equivalent electrical circuit of the coupling loop and tuning stub and the relationship to the circuit is shown in Figure 3, the same numerals being utilized to indicate the same elements shown in Figure 1.

While not wishing to be limited to any particular theory, it is believed that the action taking place when my invention is used may be as follows:

The reactance due to the self inductance of the two coupling loops 12 and 13 causes a drop in voltage along the loops and hence reduces the current in the loops and the amount of energy fed back to the cathode grid resonator. The coaxial line connected to the loops is tuned so as to present a capacitive reactance. The inductive loops and the capacitive coaxial line are tuned to resonance at the frequency for which the apparatus is designed by adjustment of the tuning ring '|6. Thus the reactive components of the circuit thus formed are neutralized and maximum current flows providing maximum feedback.

It is well known in the art that the reactance of a resonant section of high frequency transmission line at a particular frequency of operation is determined by the axial length of the section in wavelengths. A section closed 'at one end and having a length of a quarter wavelength at the operating frequency is equivalent to a parallel resonant L-C circuit with zero susceptance at that frequency, and looks like an open circuit at its open end. A half wavelength closed section is equivalent to a series resonant L-C circuit with zero reactance at the operating frequency, and looks like a short. Closed sections less than a quarter wavelength exhibit inductive reactance, while those between a quarter and a half wavelength are capacitive.

The coaxial tuning stub 'I4-16 is adjusted, by sliding the tuning ring or closure 1E axially within the outer tubular member '|5, to a length between a quarter and a half wavelength at the operating frequency, in order to give the stub a capacitive reactance. The stub length will, of course, depend upon the self inductances of the coupling loops. When the tuning stud is adjusted so that the parallel stub and loop '|2 are in series resonance with the coupling loop 13, the reactive components of the coupling loops are effectively neutralized.

In order to tune the input circuit, there is provided a tuning condenser B2 in the form of a disc or plate having a rounded periphery in order to avoid sharp edges in the high frequency field. This eliminates the corona which is experienced whenever sharp edges are used between elements at high frequency potential differences. This tuning condenser plates is slidable along the inner tubular member 4| and is operated by a gear box mechanism indicated generally at 63. A shaft 64 is rotated by means of knob 65 which in turn rotates a gear 64' coupled to the gears 66 and 61 for rotating shafts 68 and 69 threadably engaged with the tuning condenser 62 shown in Figure 2. The shaft is mounted in bearings 65 and 65". Rotation of the knob 65 moves the tuning condenser along the inner member for tuning the input circuit. This tuning condenser also shortens the line and makes the circuit more compact.

The anode voltage is brought to the anode I3 by means of a probe 'which liesalong a direct current line of force and along a, radio frequency nodal line. This probe minimizes voltage breakdown possibilities and prevents radio frequency energy from being picked up by the lead. It consists of a conducting tubular member 80 having insulating sleeve 8| and supporting a conducting lead 82 at the inner end of which is spring 38, biasing the probe point 48 into contact with the anode radiator I4.

The output is taken from the input resonator by means of the coaxial load line 51-58, the inner conductor 51 contacting tubular member 4I of the input resonator.

In order to cool the radiator and the seals of the electron discharge device, a slot 59 is provided in the outer conductor 59.

While I have indicated the preferred embodiments of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations ymay be made in the particular structure used and the purpose for which it is employed without departing from the scope of my invention as set forth in the appended claims.

I claim:

1. Apparatus for use at high frequencies comprising a cavity resonator having a predetermined resonant frequency, inputmeans coupled to said resonator for excitingthe latter and terminating in a coupling loop positioned within said resonator, said means presenting an inductive reactance in series with the inductive reactance of said loop, and -means including a capacitive element coupled in parallel with said loop and input means for tuning out the inductive reactances of said loop and input means, the parallel reactance of said tuning means and loop being capacitive and substantially equal to the inductive reactance of said input means at said resonant frequency.

2. Apparatus according to claim 1, including means for adjusting the effective capacitance of said tuning means.

3. Apparatus according to claim 1, wherein said capacitive element is a cavity resonator of adjustable length.

4. Apparatus for use at high frequencies comprising a cavity resonator resonant at a predetermined frequency and having an aperture provided fin one wall thereof, input means coupled to said resonator for exciting the latter and including a conductor extending through said aperture and,

terminating in a coupling loop within said resonator and connected to said resonator wall, said means presenting an inductive reactance in series with the inductive reactance of said loop, and means for tuning out the inductive reactances of said loop and input means including a capacitive tuning resonator connected between said resonator wall and said conductor in parallel with said loop, the parallel reactance of said tuning resontor and loop being capacitive and substantially equal to the inductive reactance of `said input means at said predetermined frequency.

5. Apparatus according to claim 4, including means for changing the effective length of said tuning resonator to adjust the effective capacitive reactance thereof at said predetermined frequency.

6. Apparatus according to claim 4, wherein said last means comprises an adjustable closure member slidable within the end of said tuning resonator.

7. Apparatus for use at high frequency including a pair of adjacent cavity resonators having a predetermined resonant frequency, means coupled thereto for exciting one of said resonators, means coupling said resonators together including a coupling loop positioned lwithin each of said resonators, and a device coupled to said means between said loops for tuning out the inductive reactance of said loops and including a capacitive reactance element.

8. Apparatus for use at high frequency including :a pair of adjacent cavity'resonators having a predetermined resonant frequency, means coupled thereto for exciting one of said resonators, means coupling said resonators together including a coupling loop positioned within and connected at one end to each of said resonators, and a device coupled to said means between said loops for tuning out the inductive reactance of said loops and including a tunable capacitive reactance element, said tunable reactance element comprising a tunable capacitive coaxial line having inner and outer conductors, the inner conductor being connected to said means between loops and the outer conductor being connected to said one of said resonators.

9. Apparatus for use at high frequencies including a pair of adjacent cavity resonators having a predetermined resonant frequency, electronic Vmeans coupled thereto for exciting one of said resonators, means coupling said resonators together including a coupling loop positioned within each of said resonators, and a device connected to said means between said loops for tuning out the inductive reactance of said loops and including a tunable capacitive reactance element, said reactance element comprising a tunable capacitive coaxial line.

10. Apparatus for use at high frequencies comprising a pair of adjacent coaxial line resonators having 1a predetermined resonant frequency and having a common wall therebetween, said wall, having an aperture, electronic means coupled to said resonators for exciting one of said resonators, a coupling element extending through said aperture and terminating in coupling loops within said resonators, and Imeans for tuning out the inductive reactance of said coupling loops and including a capacitive co'axial line tuning resonator coupled to said element between said loops and means `Within said tuning resonator for tuning the latter.

11. Apparatus for use at high frequencies including an.. electron discharge device having a. cathode, a grid and an anode, a cavity resonator 7 coupled between said cathode and grid and a second cavity resonator coupled between said grid and anode, said resonators having a predetermined resonant frequency and having a common Wall provided with an aperture, a coupling element extending through said aperture and terminating in coupling loops within said resonators and means for tuning out the inductive reactance of said coupling loops comprising a capacitive coaxial line, said coaxial line including inner and outer conductors with the inner conductor connected to said element between said loops and the outer conductor connected to said resonators.

12. Apparatus for use at high frequencies including a pair of adjacent cavity resonators having a predetermined resonant frequency and provided with a common wall, an electron discharge device extending through said common wall and having a cathode, a grid and an anode, said grid being coupled to said common wall, one of said cavity resonators being coupled between the grid and cathode and the other of said cavity resonators being coupled between the grid and the anode, aA coupling element extending between and terminating in coupling loo-ps within said cavity resonators, and means for tuning out the inductive reactance of said coupling loops including a capacitive coaxial line cavity resonator, said coaxial line resonator including inner and outer conductors, the inner conductor being connected to said element between said loops and the outer conductor being connected to said resonators.

13. Apparatus for use at high frequencies including an electron discharge device having a cathode, a grid and an anode, a coaxial line cavity resonator coupled between said cathode and grid and a second coaxial line cavity resonator coupled between said grid and anode, said resonators having a predetermined resonant frequency, being disposed end to end and having la ,common wall provided with an aperture, a coupling element extending through said aperture and terminating in coupling loops within said resonators, and means for tuning out the inductive reactance of said coupling loops comprising a tunable capacitive coaxial line, and including inner and outer conductors with the inner conductor connected to said coupling element between said loops and the outer conductor connected to said resonators.

14. Apparatus for use at high frequency including a pair of adjacent cavity resonators having a predetermined resonant frequency and provided with a common wall, an electron discharge device extending through said common wall and having a cathode, a grid and an anode, said grid being coupled to said common wall, one of said cavity resonators being coupled between said grid and cathode and the other of said cavity resonators being coupled between said grid and anode, a coupling element extending between and terminating in coupling loops within said cavity resonators, and means for tuning out the inductive reactance of said coupling loops including a capacitive third cavity resonator coupled to said element between said loops, and means within said third cavity resonator for tuning the latter.

ROBERT P. STONE.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,233,166 Hahn Feb. 25, 1941 2,281,935 Hansen et al May 5, 1942 2,284,405 McArthur May 26, 1942 2,295,680 Mouromtsei et al. Sept. 15, 1942 2,311,520 Clifford Feb. 16, 1943 2,362,209 Litton Nov. 7, 1944 2,372,193 Fisk Mar. 27, 1945 2,373,233 Dow et al Apr. 10, 1945 2,400,753 Haeff May 21, 1946 Certificate of Correction Patent No. 2,508,695 May 23, 1950 ROBERT P. STONE It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 6, line 17, for the claim reference numeral 4 read 5; line 45, before the Word loops insert said;

and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the oase in the Patent Office. Signed and sealed this 12th day of September, A. D. 1950.

[SEAL] THOMAS F. MURPHY,

Assz'sant Oommz'ssz'oner of Patents. 

